Apparatus and method for controlling adaptive circuits

ABSTRACT

A feed-forward amplifier having a signal cancellation loop including a cancellation node that includes a gain controller and a phase controller. Each controller provides a discrete tap steering signal and modulates the corresponding tap steering signal with a discrete tracer signal that takes on a preselected sequence of values. The sequence chosen so that the tracer signal is mutually orthogonal to each other tracer signal over a preselected period. A gain and phase adjuster connected to the outputs of the controllers provides a controlled gain change and phase shift in the signal cancellation loop, the magnitude of the gain change and phase shift controlled by the corresponding tap steering signals presented to the gain and phase adjuster by the controllers. A detector, the input of which is connected to the cancellation node and the output of which is connected to the controllers, outputs a measure of the envelope of the signal at the cancellation node. After the preselected period new values for the tap steering signals presented to the gain and phase adjuster by the controllers are obtained by multiplying detector output by the respective tracer signal, each over the respective preselected period, summing each resulting series of values, and changing the tap steering signals to be modulated and presented to the gain and phase adjuster in accordance with the values of the respective sums.

PRIORITY CLAIM

The present application claims priority from each of U.S. provisional patent application No. 60/311,358, filed Aug. 13, 2001 and from U.S. non-provisional patent application Ser. No. 10/016,691, filed Dec. 17, 2001, the contents of both of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to adaptive circuits. More specifically, the present invention relates to an apparatus and method for controlling adaptive circuits, such as controlling gain and phase adjustments in a feed forward amplifier circuit.

BACKGROUND OF THE INVENTION

Adaptive circuits are well known and used in a variety of applications. One well-known example of an adaptive circuit is the feed forward amplifier (“FFA”). In order to achieve linearity in a feed forward amplifier, careful control of the amplifier circuitry is required. In particular, in FFAs two or more gain and phase adjusters are often employed and the taps of each of these adjusters are carefully steered to achieve linearity through the amplifier.

Within the art of FFAs, it is known to use detector-controller circuits, one for each gain-and-phase adjuster. Each detector-controller circuit is operable to steer the taps of its respective gain-and-phase adjuster in the FFA so that the main amplifier and correctional amplifier can properly cooperate in order to reduce error introduced by the main amplifier and, should a pilot tone be used in the FFA, to also reduce the output residue of the pilot tone injected prior to the main amplifier.

In certain prior art detector-controller circuits, once the detector portion of the detector-controller circuit has indicated that the associated controller portion should make an adjustment, the controller arbitrarily steers the taps of the gain-and-phase adjuster in a direction to either increase or decrease the input to the tap, without knowing which of an increase or decrease will actually achieve the desired effect. In order to verify whether the controller steered the tap in the correct direction (e.g., to increase the signal to the tap), after the correction has been applied the detector circuit ascertains whether the direction of the variation brought about the desired effect, and, if so, instructs the controller circuit to continue steering in the same direction, if necessary. If, however, the detector circuit ascertains that the steering direction brought about an undesired result, then the detector instructs to the controller to try steering the tap in the opposite direction (e.g., to decrease the signal to the tap).

In the prior art, each detector-controller circuit works independently of each other, and therefore, achieving convergence towards an optimum level for each tap of each adjuster can be difficult. For example, rapid changes in the strength of the input signal being amplified by the FFA can make it difficult for the detector-controller circuits to respond quickly enough to converge the tap levels of each gain-and-phase adjuster towards the respective optimum levels. Furthermore, the adjustment of one tap of a gain-and-phase adjuster can disrupt an optimum or near optimum input level achieved at another tap, therefore cascading disruptions through all of the taps.

The inventor of the present invention also believes that a further problem is that such prior art controller circuits can sometimes result in taps being steered to levels that are levels corresponding to local minima for the input signal, missing a global optimum for the input signal.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel apparatus and method for controlling an adaptive circuit that obviates or mitigates at least one of the above-identified disadvantages of the prior art. It is a further object of the present invention to provide a novel feed forward amplifier that obviates or mitigates at least one of the above-identified disadvantages of the prior art.

According to an aspect of the present invention, there is provided a feed-forward amplifier having a signal cancellation loop including a cancellation node that includes a gain controller and a phase controller. Each controller provides a discrete tap steering signal and modulates the corresponding tap steering signal with a discrete tracer signal that takes on a preselected sequence of values. The sequence chosen so that the tracer signal is mutually orthogonal to each other tracer signal over a preselected period. A gain and phase adjuster connected to the outputs of the controllers provides a controlled gain change and phase shift in the signal cancellation loop, the magnitude of the gain change and phase shift controlled by the corresponding tap steering signals presented to the gain and phase adjuster by the controllers. A detector, the input of which is connected to the cancellation node and the output of which is connected to the controllers, outputs a measure of the envelope of the signal at the cancellation node. After the preselected period new values for the tap steering signals presented to the gain and phase adjuster by the controllers are obtained by multiplying detector output by the respective tracer signal, each over the respective preselected period, summing each resulting series of values, and changing the tap steering signals to be modulated and presented to the gain and phase adjuster in accordance with the values of the respective sums. Optionally, each tap steering signal may be increased or decreased depending upon the polarity of the corresponding sum, or the tap steering signal presented to the gain and phase adjuster is left unchanged if the corresponding sum is zero or within a preselected range about zero but, if the corresponding sum is outside the preselected range about zero, is increased or decreased depending upon the polarity of the corresponding sum. Also, each tap steering signal is increased if the corresponding sum is positive and decreased if the corresponding sum is negative. In any of the embodiments discussed above, the tracer signals vary in polarity but not in magnitude and may be chosen to be pseudo noise sequences or Walsh codes.

According to another aspect of the present invention, there is provided a feed-forward amplifier that includes:

-   -   an input port;     -   a first main path splitter, the input of which is connected to         the input port so that when an input signal applied to the input         port it is split by the first main path splitter into a main         signal and a feed-forward signal;     -   a main signal path gain and phase adjuster, the input of which         is connected to the first output of the first main path         splitter, the main signal path gain and phase adjuster having a         gain-control input tap and a phase-control input tap configured         so that the voltage levels on the taps control the amplitude and         phase of the main signal;     -   a main amplifier, the input of which is connected to the output         of the main signal path gain and phase adjuster;     -   a second main path splitter, the input of which is connected to         the output of the main amplifier;     -   a feed-forward signal path delay element, the input of which is         connected to the second output of the first main path splitter,         the delay imposed by the feed-forward signal path delay element         selected to approximately match the delay in the main signal         caused by the main amplifier;     -   a feed-forward path coupler, the first input of which is         connected to the output of the feed-forward signal path delay         element;     -   a connector/attenuator connecting the second output of the         second main path splitter to the second input of the         feed-forward path coupler, the attenuation selected so that the         undistorted portion of the main signal provided to the         feed-forward path coupler is approximately cancelled out by the         feed-forward signal;     -   a feed-forward path splitter, the input of which is connected to         the output of the feed-forward path coupler;     -   a detector, the input of which is connected to the second output         of the feed-forward path splitter;     -   a gain controller, the input of which is connected to the output         of the detector and the output of which is connected to the         gain-control input tap; and     -   a phase controller, the input of which is connected to the         output of the detector and the output of which is connected to         the phase-control input tap,         wherein:

-   each of the controllers modulates the voltage level on its     respective output with a discrete low level signal that takes on a     preselected sequence of values, the sequence chosen so that each low     level signal is mutually orthogonal to each other low level signal     over a preselected period; the detector outputs a measure of the     envelope of the signal at the cancellation node; and each controller     multiples the signal received from the detector by the low level     signal with which it modulated the tap to which it is connected, in     each case over the preselected period, sums the resulting series of     values over time, and changes the voltage level on its respective     tap in accordance with the value of the sum.

Optionally, each voltage level is increased or decreased depending upon the polarity of the corresponding sum or the voltage level presented to the gain and phase adjuster is left unchanged if the corresponding sum is zero or within a preselected range about zero but, if the corresponding sum is outside the preselected range about zero, is increased or decreased depending upon the polarity of the corresponding sum. Also, each voltage level may be increased if the corresponding sum is positive and decreased if the corresponding sum is negative and each output voltage level may be changed in proportion to magnitude of the respective sum.

In any of the embodiments discussed above, the low level signals vary in polarity but not in magnitude and the low level signals may be chosen to be pseudo noise sequences or Walsh codes.

According to yet another aspect of the present invention, there is provided a feed-forward amplifier having a signal cancellation loop including a cancellation node at which a signal is to be minimized, including:

-   a controller for providing a tap steering signal and modulating the     tap steering signal with a tracer signal that takes on a preselected     sequence of values; -   an adjuster connected to the output of the controller for providing     a controlled change in a characteristic of the signal cancellation     loop that results in a change in a measure of the envelope of the     signal at the cancellation node, the magnitude of the change in the     characteristic controlled by the modulated tap steering signal     presented to the adjuster by the controller; and -   a detector, the input of which is connected to the cancellation node     and the output of which is connected to the controller, the detector     for outputting the measure of the envelope of the signal at the     cancellation node, -   wherein after the preselected period a new setting for the tap     steering signal is obtained by multiplying the detector output by     the tracer signal, summing the resulting series of values, and     changing the tap steering signal to be modulated and provided to the     adjuster in accordance with the value of the sum.

Optionally, the tap steering signal may be increased or decreased depending upon the polarity of the corresponding sum, or the tap steering signal presented to the gain and phase adjuster is left unchanged if the corresponding sum is zero or within a preselected range about zero but, if the corresponding sum is outside the preselected range about zero, is increased or decreased depending upon the polarity of the corresponding sum. Also, the tap steering signal is increased if the corresponding sum is positive and decreased if the corresponding sum is negative. In any of the embodiments discussed above, the tracer signal vary in polarity but not in magnitude and may be chosen to be pseudo noise sequences or Walsh codes.

According to yet another aspect of the present invention, there is provided a circuit having a node at which a signal is adaptively minimized by the circuit, comprising: a controller providing an output voltage level, the output voltage level modulated by a low level signal that takes on a preselected sequence of values over a preselected period; an adjuster connected to the output of the controller for providing a controlled change in a characteristic of the adaptive circuit that results in a change in a measure of the envelope of the signal at the node, the magnitude of the change in the characteristic controlled by the voltage level presented to the adjuster by the controller; and a detector, the input of which is connected to the node and the output of which is connected to the controller, the detector outputting the measure of the envelope of the signal at the node, wherein after the preselected period a new setting for the voltage level presented to the adjuster by the controller is obtained by multiplying the detector output by the low level signal, summing the resulting series of values, and changing the voltage level presented to the adjuster in accordance with the value of the sum.

Optionally, each voltage level is increased or decreased depending upon the polarity of the corresponding sum or the voltage level presented to the adjuster is left unchanged if the corresponding sum is zero or within a preselected range about zero but, if the corresponding sum is outside the preselected range about zero, is increased or decreased depending upon the polarity of the corresponding sum. Also, each voltage level may be increased if the corresponding sum is positive and decreased if the corresponding sum is negative and each output voltage level may be changed in proportion to magnitude of the respective sum.

According to yet another aspect of the present invention, there is provided a feed forward amplifier comprising:

an amplifier portion including a coupler, first and second gain and phase adjusters, first and second delay elements, a main amplifier and a correctional amplifier, the coupler providing an input signal to said amplifier portion to a first signal path including the first gain and phase adjuster, the main amplifier and the first delay element and an output and the coupler providing the input signal to a second signal path including the second delay element, the second gain and phase adjuster and the correctional amplifier having a first signal path for carrying an input signal to a first gain-and-phase adjuster and a main-amplifier, said first gain-and-phase adjuster having a pair of taps for steering said first adjuster, said amplifier portion having a second signal path for carrying a sample of said input signal generated to a second gain-and-phase adjuster and a correctional-amplifier, said second gain-and-phase adjuster having a pair of taps for steering said adjuster; and

a detector-controller portion having a first detector for receiving a detected signal from said first signal path and a second detector for receiving a detected signal from said second signal path, said detector-controller portion further comprising a first pair of controllers for receiving said detected signal from said first detector and a second pair of controllers for receiving said detected signal from said second detector, said controllers each operable to steer a respective one of said taps based on said received detected signals, each of said controllers further operable to inject tracer-signals into its respective tap, said tracer-signals for carrying through said amplifier portion and modulating said detected signals, said controllers each operable to extract from its respective detected signals a tap-signal by using its respective said tracer-signal, said controllers each further operable to utilize said extracted tap-signal to determine a desired direction for steering its respective tap and to output, substantially simultaneously with each other controller, a signal to steer said respective tap.

According to yet another aspect of the present invention, there is provided a feed forward amplifier comprising: an amplifier portion including:

-   -   (a) a first signal path having a first gain and phase adjuster,         a main amplifier and a delay element; and     -   (b) a second signal path having a delay element, a second gain         and phase adjuster and a correctional amplifier, each gain and         phase adjuster including a control input tap to accept an input         to alter the phase response of the gain and phase adjuster and a         control input tap to accept an input to alter the gain response         of the gain and phase adjuster, the first and second signal         paths having a common signal input and a common signal output;         and         a detector portion including:     -   (c) a first detector to receive a signal from the common signal         output and to provide the received signal to a first controller         operable to create an input to the gain tap of the second gain         and phase adjuster and to provide the received signal to a         second controller operable to create an input to the phase tap         of the second gain and phase adjuster; and     -   (d) a second detector to receive a signal from the second signal         path before the second gain and phase adjuster and to provide         the received signal to a first controller operable to create an         input to the gain tap of the first gain and phase adjuster and         to provide the received signal to a second controller operable         to create an input to the phase tap of the first gain and phase         adjuster, each controller responsive to a component in said         received signals which is orthogonal to the components to which         each other controller are responsive to and all the created         inputs being applied to the taps substantially simultaneously         and altering the operation of said feed forward amplifier to         linearize the amplification of the input signal through the feed         forward amplifier.

According to yet another aspect of the present invention, there is provided a method for operating an adaptive control circuit having a plurality of control input taps, said method comprising, for each said control input, the steps of: detecting a signal, including a tracer signal, from said circuit; extracting a measurement from the tracer signal in said detected signal; determining an appropriate input to be applied to said control input to improve operation of said adaptive circuit; creating a tracer signal for said control input, said created tracer signal being orthogonal to the tracer signals created for each other control input; and combining said tracer signal and said determined input and applying the resulting signal to said control input.

An apparatus and method for operating an adaptive circuit includes injecting a set of orthogonal tracer signals into the circuit. The tracers' signals are extracted after modification during operation of at least a portion of the circuit and are examined by respective controllers to modify operation of the circuit.

In one embodiment, the invention is incorporated into a feed forward amplifier in which a set of orthogonal tracer signals is applied to the amplifier. A detector controller detects a signal including as components the orthogonal tracer signals as modified by portions of the amplifier. Each controller portion of the detector controller extracts a measurement relative to its respective tracer signal from the detected signal and modifies its output to control a portion of the amplifier accordingly. The controllers apply their outputs to the respective portions of the amplifier at substantially the same time, leading to quick convergence of the operating point of the amplifier to an optimal, or near-optimal, configuration. Injection of the tracer signals into the amplifier is accomplished by dithering the controller outputs by the respective orthogonal tracer signals.

According to yet another aspect of the present invention, there is provided an adaptive circuit comprising:

at least two adjusters, each adjuster including at least one control input to alter the operation of the circuit;

at least one signal generator to create at least one tracer signal, each created tracer signal being orthogonal to each other created tracer signal;

at least two controllers, each controller operable to output a control signal to at least a respective one of the control inputs of the at least two adjusters, a different orthogonal tracer signal from said at least one signal generator being applied to each respective control signal as a dither; and

at least one detector operable to extract a composite signal from the circuit and to apply the composite signal to the at least two controllers, each controller being responsive to the applied signal to extract at least one orthogonal tracer and alter the respective control signal to converge operation of the circuit to an optimal or near optimal configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein:

FIG. 1 is a block diagram of a feed forward amplifier in accordance with an embodiment of the present invention;

FIG. 2 is a block diagram of a detector-controller portion of the amplifier shown in FIG. 1;

FIG. 3 is a flow chart showing a method of controlling the gain and phase adjustment of the amplifier of FIG. 1;

FIG. 4 is an exemplary set of Walsh codes for use in the detector-controller portion of the amplifier of FIGS. 1 and 2;

FIG. 5 shows an example of the operation of two of the controllers shown in FIG. 2 using the method of FIG. 3, during an initial power-on of the amplifier of FIG. 1; and

FIG. 6 shows an example of the operation of the controllers shown in FIG. 5 during a subsequent iteration through the method shown of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1, a forward feed amplifier (“FFA”) in accordance with an embodiment of the invention is indicated generally at 20. FFA 20 comprises an amplifier portion 24 and a detector-controller portion 28. Amplifier portion 24 includes a coupler 36 that is connected to an input signal path 40. Coupler 36 is operable to split an incoming signal from path 40 into a main amplifier signal path 44 and a correctional amplifier signal path 48.

Main amplifier signal path 44, which carries the main signal from coupler 36, includes a gain and phase adjuster GPA₁, a main amplifier 56 and a delay element 60 that outputs to an output signal path 64. GPA₁ includes a gain control input tap T₁, and a phase control input tap T₂, each of which can be steered so that GPA₁ operates to yield maximum signal cancellation at the output of coupler 82 and the input of coupler 104, as discussed below. The location in the circuit at which maximum signal cancellation is to occur is sometimes referred to as the “cancellation node”.

Correctional amplifier signal path 48 which carries a sample, generated by coupler 36, of the signal from input signal path 40 includes a delay element 68, a gain and phase adjuster GPA₂ and a correctional amplifier 74, the output of which connects to output signal path 64 via a coupler 76. GPA₂ includes a gain control input tap T₃, and a phase control input tap T₄, each of which can be steered so that GPA₂ is adjusted to require a minimum, or near minimum, amount of power to be delivered to the correctional amplifier 74. As used herein, the terms “steer”, “steered” and “steering” are intended to comprise all suitable methods of adjusting and/or controlling of the taps respective to a gain and phase or other suitable adjuster. In the embodiment of the invention discussed below, taps T₁, T₂, T₃, and T₄, are steered by changing the voltage levels applied to each of them respectively.

As will be apparent to those of skill in the art, GPA₂ and correctional amplifier 74 form an error pathway 73 within amplifier portion 24. Accordingly, when the output of correctional amplifier 74 is coupled to the output of delay 60, errors and pilot tones, if used, are substantially eliminated from the output signal path 64, such that the output signal path 64 presents a substantially linear amplification of the signal from input signal path 40.

Amplifier portion 24 is further characterized by a coupled path 79 that interconnects a first coupler 80, which is connected to the output of main amplifier 56, and a second coupler 82, which is connected to the output of delay element 68, in order to provide a sample of the error introduced by main amplifier 56 to the error pathway 73, commencing at GPA₂. Attenuation may be provided in coupled path 73, if not already provided by the first coupler 80.

The main amplifier signal path 44, the correctional amplifier signal path 48, and the coupled path 79 together are sometimes referred to as a “signal cancellation loop”.

In the illustrated embodiment, amplifier portion 24 further includes a pilot tone generator 86 that is coupled, via a coupler 90, to the input of main amplifier 56. Pilot tone generator 86 generates a pilot tone for use by error pathway 73 in the usual manner for reducing error introduced by main amplifier 56. By the same token, amplifier portion 24 further includes a pilot tone receiver 94 that is coupled, via a coupler 98, to output signal path 64. Pilot tone receiver 94 is operable to measure any remaining pilot tone present along output signal path 64 for eventual use by error pathway 73 to introduce a signal at coupler 76 that will reduce the pilot tone in output signal path 64.

Detector-controller portion 28 connects to amplifier portion 24 through various inputs and various outputs, as described herein. Specifically, a coupler 104 connected just prior to error pathway 73 delivers an input signal to a first detector D₁, which in turn presents a detector-output to a gain controller C₁ and a phase controller C₂. In the illustrated embodiment, the detector-output is a measure of the amplitude of the envelope of the input signal applied to it. However, it is within the scope of the invention to provide as a detector-output a signal proportional to the log of the RMS value of the envelope of the input signal or proportional to peaks of the envelope of the input signal, as well as any other measure or signal that will occur to those skilled in the art. Wherever in the following or in the claims that reference is made to the detector-output being the amplitude of the envelope of the input signal applied to it, it should be understood that such other signals or measures are also intended.

Similarly, pilot tone receiver 94 delivers an output signal to a second detector D₂, which in turn presents a detector-output to a gain controller C₃ and a phase controller C₄. Again, detector D₂ outputs the amplitude of the envelope of the input signal applied to it. As will be discussed in greater detail below, controllers C₁, C₂, C₃ and C₄ are operable to steer taps T₁, T₂, T₃ and T₄, respectively, based on the signals received from their respective detectors D, in order to find optimum (or otherwise desired) gain and phase adjustments for each of adjusters GPA₁ and GPA₂.

In the illustrated embodiment, tracer signals are applied to each of main amplifier signal path 44 and correctional amplifier signal path 48 by using them to modulate the voltage levels applied to the taps T₁, T₂, T₃, and T₄, respectively. Those voltage levels are also referred to as tap steering signals and the modulated voltage levels as modulated tap steering signals. Each tracer signal, because it rapidly but slightly changes either the gain or the phase in the signal cancellation loop, causes variations in the amplitude of the envelope of the input signal applied to one of the detectors D₁ and D₂. The detected amplitudes of the envelopes of the signals applied to the detectors D₁ and D₂ are passed to the respective controllers C. Each controller C extracts the variation in the detector output caused by the tracer signal applied to the corresponding tap and steers the tap accordingly. The variations in the detector outputs caused by the tracer signals can be separated from each other because each tracer signal is selected to be orthogonal to each other tracer signal. As described below, to achieve orthogonality in the illustrated embodiment each tracer signal is a Walsh code, but other techniques, such as selecting appropriate pseudo noise sequences as the tracer signals will be apparent to those of skill in the art. As will become apparent to those of skill in the art from the discussion herein, the present invention will operate with tracer signals that are not totally orthogonal to each other, although better performance will be obtained when using signals as orthogonal as possible. Accordingly, as used herein, the term orthogonal is intended to include both perfectly orthogonal signals, such as Walsh codes, and near-orthogonal signals, for example pseudo noise sequences taken over a time period that provides approximately orthogonal results. The general criterion is that the more uncorrelated tracer signals are over an appropriate time period the better the results.

Before going into the details, as an overview, consider an idealized situation that may help in understanding the embodiment of the invention described herein. To aid in understanding, we assume that the main amplifier does not distort the input signal at all and we start with adjusting only one tap steering signal. We begin by setting a tap steering signal at a particular voltage level. If that voltage level is applied to a tap of an adjuster, a particular level of signal cancellation at the cancellation node results. If the voltage level is optimal (so that the amplitude of envelope of the signal at the cancellation node is zero), dithering of the voltage level by a tracer signal that has an average value of zero (as do orthogonal and pseudo noise sequences over appropriate periods) will result in slight excursions in the amplitude of envelope of the signal at the cancellation node above and below zero, but the sum of all the excursions will be zero. Now suppose that the voltage level is not optimal. Then the slight excursions in the amplitude of the envelope of the signal at the cancellation node will be to levels above and below the amplitude of envelope of the signal at the cancellation node that would occur if no dither were applied. The result will be a non-zero sum with a polarity, or sign, the same as the polarity of the amplitude of the envelope of the signal at the cancellation node would be if no dither were applied. So far we have assumed that there is only one tap. If there are more taps, then by using orthogonal or pseudo noise sequences over appropriate periods as tracer signals, the excursions in the amplitude of envelope of the signal at the cancellation node caused by dithering of each tap can be extracted separately from the amplitude of envelope of the signal at the cancellation node, summed, and used to adjust the corresponding tap steering signals simultaneously.

Referring now to FIG. 2, detector-controller portion 28 will now be discussed in greater detail. As shown, controllers C₁, C₂, C₃ and C₄ each include the same components. Each controller C includes a multiplier 200 that receives a detector-output from a respective detector D. Controllers C are operable to utilize the detector-output to determine how to steer their respective tap T. In the present embodiment, each detector-output is the amplitude of the envelope of the signal received by a respective detector D and carries combined information about the effects of dithering (modulating) the respective tap steering signals with the respective tracer signals on the amplitude of the envelope of the signal received by the respective detector D. The information carried about the effect of the dithering of each tap steering signal with a tracer signal may be separately extracted from the detector-output in the manner discussed in greater detail further below.

To extract the effect of the tracer signal injected by tap T for the controller C, each multiplier 200 receives its Walsh code from a Walsh code generator 204. Each Walsh code generator 204 ₁, 204 ₂, 204 ₃ and 204 ₄, generates a unique Walsh code, which, as is understood by those of skill in the art, is a preselected pattern of one or more logical ones and/or logical zeroes that repeat over a given period and is orthogonal to each other Walsh code. As will be discussed in greater detail below, when the detector-output from a respective detector D is multiplied by multiplier 200 with a respective Walsh code, only the portion of the detector-output resulting from the tracer signal injected at the respective tap T will be output from the respective multiplier 200.

Controllers C also each include an integrator 208 which is operable to sum the results from multiplier 200, which represent the effect of tracer signal for the respective tap T on the respective detector-output, for each period and output those summed results to an adjuster 212 which is operable to determine from the summed result whether the tap T it is responsible for is properly steered. If an adjuster 212 determines that its corresponding tap T was steered in the proper direction, then adjuster 212 outputs a signal that continues to steer that tap T in the same direction. If adjuster 212 determines that its corresponding tap T was steered in the wrong direction, then adjuster 212 outputs a signal that steers that tap T in the opposite direction. Adjuster 212 can also determine that the tap T is at an optimum level, in which case adjuster 212 does not steer tap T at all, but leaves the tap steering signal at the existing level. Further details of adjuster 212 will be discussed in greater detail below.

To inject the tracer signal for a controller C into amplifier portion 24, the signal outputted from adjuster 212 is modulated, using a summer 216, with the Walsh code generated at Walsh code generator 204, the Walsh code having first been attenuated through an attenuator 220 by a factor A. The Walsh code is attenuated, by factor A, to a level that provides a suitable “dither” or “perturbance” that can be summed with the control signal from adjuster 212 for the respective tap T. The voltage level of the resulting modulated signal is at a level that will generally yield a minimum reliably detectable signal at the output of detector D.

As will be apparent to those of skill in the art, in order for the Walsh code to behave as a good dither, each Walsh code for each controller C is selected to have as many transitions as possible, while still being orthogonal to the Walsh codes of the other controllers C. Also, as the tracer signal is averaged over a suitable period of time to reduce the effects of noise in the detected signal, it is desired to choose a Walsh code, or other orthogonal signal, with a suitably long length. It is presently preferred that a length for the Walsh codes is selected which is at least twice the number taps T to be controlled, i.e.—in the embodiment of FIG. 1, the shortest desired length of Walsh codes would be an eight chip code and, in fact, it is presently preferred to use a Walsh code length of sixty-four chips for a feed forward amplifier with four taps T.

The output of each summer 216 is then presented to its respective tap T, thereby steering each respective tap T accordingly and injecting the respective tracer signal.

A method of controlling the gain and phase adjustment of feed forward amplifier 20 will now be discussed with reference to FIG. 3. The flow-chart in FIG. 3 shows a sequence of steps which can be used to operate, for example, each controller C of detector-controller portion 28, thereby steering each tap T. In other words, the sequence of steps in FIG. 3 will be performed, in parallel, for each controller C.

Although, as mentioned above, in a presently preferred embodiment each Walsh code is actually sixty-four chips in length, for simplicity while explaining the method, it will be assumed that each Walsh code W₁, W₂, W₃ and W₄, is only eight chips in length. Each Walsh code W₁, W₂, W₃ and W₄ is generated by a respective Walsh code generators 204 ₁, 204 ₂, 204 ₃ and 204 ₄ and is shown in Table I and illustrated in the pulse-waveforms shown in FIG. 4. From the waveforms shown therein, it is to be understood that a “1” means a logical “1”, and “−1” means a logical “0”.

TABLE I Chip W₁ W₂ W₃ W₄ 1 1 1 1 1 2 −1 −1 1 −1 3 −1 1 −1 −1 4 1 −1 −1 1 5 −1 1 1 1 6 1 −1 1 −1 7 1 1 −1 −1 8 −1 −1 −1 1

Again for simplicity, the method of FIG. 3 will only be discussed in detail with reference to controllers C₁ and C₂ and their associated detector D₁. The method begins at step 300 where a signal is detected at detector D₁ from the amplifier portion 24 of feed forward amplifier 20. To illustrate how this step can be accomplished according to a present embodiment, it will be assumed that feed forward amplifier 20 has just been activated (i.e. initialized), but that no input signal is present along input signal path 40, and accordingly no output signal is present along output signal path 64.

The activity in feed forward amplifier 20 at this point in the method is illustrated in FIG. 5, where detector D₁, controller C₁ and controller C₂ are shown. As there is no input signal along input signal path 40, detector D₁ detects this and outputs a corresponding waveform, which is represented in FIG. 5 as a detector-output waveform 400 a, which in turn is inputted into multiplier 200 ₁ and multiplier 200 ₂.

By way of further background to the operation of the present embodiment, it will be apparent to those of skill in the art that the tracer signal being applied to the taps T of gain and phase adjuster GPA₁, whether a Walsh code or any other dither, will only be detectable at detector D₁ where there is an input signal along input signal path 40 as the tracer signal is a modulation of the input signal. Similarly, if a pilot tone is being injected at coupler 90, then the tracer signal applied at the taps T of GPA₂ will be detectable at detector D₂ as modulation of the pilot tone detected at detector D₂. As there is as yet no input signal in FIG. 5, detector-output waveform 400 a is all zeros, as shown.

Referring again to FIG. 3, the method then advances to step 320 where the tracer signal for the tap T₁ respective to the controller C₁ is extracted from the signal detected at step 300. In a present embodiment, this signal is extracted from detector-output waveform 400 a using multiplier 200 and integrator 208. First, multiplier 200 multiplies the Walsh code output from Walsh code generator 204 with the detector-output waveform 400 a to extract the tracer signal. The product waveform is presented to integrator 208, which sums each pulse in the waveform over the number of chips in the Walsh code. The output for each integrator 208 ₁, 208 ₂ are represented on FIG. 5 as items 404 a ₁ and 404 a ₂, respectively.

Specifically, for controller C₁, since the detector-output 400 a={0, 0, 0, 0, 0, 0, 0, 0 }, and since the output of Walsh code generator 204 ₁ can be represented by the series W₁={1, −1, −1,1,−1,1,1,−1}, then the output of multiplier 200 ₁ can be represented as {0, 0, 0, 0, 0, 0, 0, 0}×{1, −1, −1, 1, −1, 1, 1, −1}=(0, 0, 0, 0, 0, 0, 0, 0). The result 404 a ₁, from integrator 208 ₁ can be represented as 404 a ₁=(0, 0, 0, 0, 0, 0, 0, 0)=0.

Similarly, for controller C₂, since detector-output 400 a={0, 0, 0, 0, 0, 0, 0, 0} and since the output of Walsh-code generator 204 ₂ can be represented by the series W₂={1, −1, 1, −1, 1, −1, 1, −1}, then the output of multiplier 200 ₂ can be represented as {0, 0, 0, 0, 0, 0, 0, 0}×{1, −1, 1, −1, 1, −1, 1, −1}=(0, 0, 0, 0, 0, 0, 0, 0). The result 404 a ₂, from integrator 208 ₂ can be represented as 404 a ₂=(0, 0, 0, 0, 0, 0, 0, 0)=0.

Referring again to FIG. 3, the method then advances to step 340 where the appropriate steering signal for the tap T_(i) respective to a given controller C_(i) is determined. In the present embodiment, this step is performed by adjuster 212. Continuing with the above example being discussed with reference to FIG. 5, the result 404 a from each integrator 208 is then passed to its respective adjuster 212. As shown in the example of FIG. 5, the result 404 a from each integrator 208 was “0”, and this value is passed to adjuster 212.

In the present embodiments, adjuster 212 includes digital signal processing circuitry that is operable to make the determination of whether and how to steer the tap T based on the result 404 a passed from its respective integrator 208. Adjuster 212 determines from the received “0” input that no steering of a tap T is required and the method advances to step 360, wherein no adjustment is made to the steering signal applied to the respective tap T.

If adjuster 212 had received a positive or negative input from the result 404 a, then an appropriate adjustment to the tap steering signal would be determined and the method would have advanced to step 360 where the appropriate adjustment of the steering signal is applied to the respective tap T.

Continuing with the example being discussed in conjunction with FIG. 5, as it was determined at step 340 that no adjustment to the steering signal was required, and as feed forward amplifier 20 has just been activated, adjuster 212 determines that the tap T for its respective controller C should remain in its nominal position. Each adjuster 212 then outputs a corresponding tap steering signal, indicated on FIG. 5 as signals 408 a ₁ and 408 a ₂. The exact format of tap steering signals 408 can be generated using known means and circuitry and need only correspond with the format required to control the specific type of gain and phase adjusters used within amplifier portion 24.

Tap steering signals 408 a are then presented to their respective summer 216, which sums the tap steering signal 408 a with an attenuated version AW of the Walsh code W. This attenuated Walsh code is indicated on FIG. 5 as items AW₁ and AW₂ and is the tracer signal to be injected in the signal paths of amplifier portion 24 for the next iteration of the control method. It will be apparent to those of skill in the art that the factors A for each attenuator 220 can differ from each other. Attenuated Walsh codes AW are attenuated by factors A to a level, appropriate for the specific GPA employed, so they act as a “dither” modulated on top of its tap steering signal 408 a and that operation of the gain and phase GPA is not impeded by the dither.

Attenuated Walsh codes AW are produced by attenuators 220, which simply receive the output of their respective Walsh code generator 204 and generate and output an attenuated version thereof to their respective summers 216. Thus, each tap steering signal 408 a and respective attenuated Walsh code AW are combined by their respective summer 216, to create a dithered tap steering signal, indicated on FIG. 5 as items 412 a ₁ and 412 a ₂. At step 360, the dithered tap steering signals 412 a ₁, 412 a ₂ are then presented to their respective taps T₁, T₂ of GPA₁ and the method then returns to step 300, where another iteration of the method begins.

As mentioned above, the method shown in FIG. 3 operates simultaneously for detector D₂ and controllers C₃ and C₄ in the same manner as that described above for detector D₁ and controllers C₁ and C₂. Thus, steering adjustments can be effected at each tap T at the same time.

An example of a second iteration through the method of FIG. 3 will now be discussed with reference to FIG. 6. It is assumed that, prior to this iteration an input signal is being input along input signal path 40. FIG. 6 again shows detector D₁ and controllers C₁ and C₂. This iteration commences with step 300 again being performed by detector D₁. As there is now an input signal along input signal path 40, detector D₁ now detects the tracer signal (dither) that has been applied to at least one of the gain and phase adjusters and reflects this detection in detector-output waveform 400 b. For purposes of explaining the present embodiment, it will be assumed that detector-output waveform 400 b is {−3, −1, 0, 2, −3, 0, −1, 1} and waveform 400 b is input to multipliers 200 ₁ and 200 ₂.

Referring again to FIG. 3, the method then advances to step 320 where the tap measurement for the tap T_(i) respective to the controller C_(i) is extracted from the signal detected at step 300. In the present example discussed in conjunction with FIG. 6, this signal is extracted from detector-output waveform 400 b using multiplier 200 _(i) and integrator 208 _(i) of each controller C_(i). First, multiplier 200 multiplies the Walsh code output from Walsh code generator 204 with the detector-output waveform 400 b. The product waveform is then presented to integrator 208, which sums each pulse in the waveform over the number chips in the Walsh code. The results from each integrator 208 ₁, 208 ₂ are represented on FIG. 6 as items 404 b ₁ and 404 b ₂, respectively.

Specifically, for controller C₁, since the detector-output 400 b={−3, −1, 0, 2, −3, 0, −1, 1}, and since the output of Walsh-code generator 204 ₁ W₁={1, −1, −1, 1, −1, 1, 1, −1}, then the output of multiplier 200 ₁ can be represented as {−3, −1, 0, 2, −3, 0, −1, 1}×{1, −1, −1, 1, −1, 1, 1, −1}=(−3, 1, 0, 2, 3, 0, −1, −1). The result for integrator 208 ₁ can be represented as 404 b ₁=(−3, 1, 0 2, 3, 0, −1, −1)=1. Similarly, for controller C₂, 400 b={−3, −1, 0, 2, −3, 0, −1, 1} and since the output of Walsh-code generator 204 ₂ W₂={1, −1, 1, −1, 1, −1, 1, −1}, then the output of multiplier 200 ₂ can be represented as {−3, −1, 0, 2, −3, 0, −1, 1}×{1, −1, 1, −1, 1, −1, 1, −1}=(−3, 1, 0, −2, −3, 0, −1, −1). The result for integrator 208 ₂ can be represented as 404 b ₂=(−3, 1, 0, −2, −3, 0, −1, )=−9.

The method then advances to step 340 where the appropriate steering signal for the tap T respective to a given controller C is determined. Continuing with the above example being discussed with reference to FIG. 6, the result 404 b for each integrator 208 is then passed to its respective adjuster 212. In this example, the result 404 b ₁ produced by integrator 208 ₁ was “1” and this value is passed to adjuster 212 ₁. The result 404 b ₂ produced by integrator 208 ₂ was “−9”, and this value is passed to adjuster 212 ₂. In each case, the sign of the integrator output determines which way the respective tap T is adjusted.

As previously discussed, adjusters 212 include digital signal processing circuitry which is operable to make the determination of whether to steer the tap T based on the result 404 b passed from its respective integrator 208. In the present embodiment, adjusters 212 are configured so that, if the received input from its respective integrator 208 does not equal “0”, then it is determined that steering of its respective tap T is required. Accordingly, in the example of FIG. 6 adjusters 212 ₁ and 212 ₂ both determine that steering of the respective taps T₁, T₂ is required.

For controller C₁, adjuster 212 ₁ has received a “1”, and thereby determines that the tap steering signal 408 b ₁ to tap T₁ should be increased and accordingly, the output tap steering signal 408 b ₁ is increased by a preselected increment from the previous signal that was used during the previous iteration through the method of FIG. 3. For controller C₂, adjuster 212 ₂ has received a “−9”, and thereby determines that the tap steering signal 408 b ₂ to tap T₂ should be decreased and accordingly, the output tap steering signal 408 b ₂ is decreased by a preselected increment from the previous signal that was used during the previous iteration through the method of FIG. 3. Tap steering signals 408 b are then presented to their respective summer 216, which sums the tap steering signal 408 a with the respective attenuated Walsh code AW. Thus, each tap steering signal 408 a and attenuated Walsh code AW are summed together by their respective summer 216, to create a dithered tap steering signal, indicated on FIG. 6 as items 412 b ₁ and 412 b ₂. The dithered tap steering signals 412 b are then presented to their respective taps T of their respective GPA at step 360.

Iterations through the method of FIG. 3 repeat continuously for each controller C, increasing or decreasing each tap output signal 412 until an optimum level for a respective tap T is reached, at which point the respective controller C simply maintains the tap output signal 412 at its current level (i.e.—the result from integrator 208 of the product from multiplier 200 of waveform 400 and Walsh code W is “0”) until, during a subsequent iteration through the method of FIG. 3, further steering of the respective tap T is required.

While the embodiments discussed herein are directed to specific implementations of the invention, it will be understood that combinations, sub-sets and variations of the embodiments are within the scope of the invention. For example, it will now be apparent to those of skill in the art that amplifier portion 24 is a substantially known configuration for one type of amplifier portion of a feed forward amplifier, yet other configurations of amplifier portion 24 are within the scope of the invention. Other such configurations are discussed in a co-pending U.S. patent application Ser. No. 09/715,085, assigned to the assignee of the present invention, the contents of which are incorporated herein by reference. In particular, this application teaches a feed forward amplifier with a single pilot tone generator receiver, which is also suitable for incorporation into the present invention. A general discussion of feed forward amplifiers instructive to those of skill in the art for the design of amplifier portions is discussed in U.S. Pat. No. 3,471,798, the contents of which are also incorporated herein by reference.

As will also be apparent to those of skill in the art, feed forward amplifiers can include more than two gain and phase adjusters. In such a case, a detector-controller circuit can be employed for each gain and phase adjuster and a separate orthogonal tracer signal employed for each tap T.

Further, while the embodiments discussed herein refer specifically to FFAs having a pilot tone, it is to be understood that the present invention is also applicable to FFAs that do not use pilot tone, but use some other method, for example such as measuring intermodulation energy at detector D₂.

While the embodiments discussed herein refer to gain and phase adjusters having gain and phase taps T, it is to be understood that the present invention is not so limited and can be applied to other types of adjusters, such as phase and gain adjusters having in phase ‘T’ and quadrature “Q” taps. Furthermore, while the embodiments discussed herein refer to controlling gain and phase adjustments in FFAs, it is to be understood that the apparatus and method discussed herein can be modified for use with any appropriate circuit where adaptive control is used, such as feed forward circuits, etc.

It is also to be understood that while the embodiments discussed herein refer to Walsh codes, any type of orthogonal tracer-signal, such as suitable length pseudo noise sequences or the like can be used, with appropriate modifications to other aspects of the remainder of the circuit. Additionally, while the number of chips of the Walsh codes used in the exemplary embodiments discussed herein corresponds to the period of the pulse wave-form of the detector-output, it will be understood that these periods need not correspond at all. In general, it is to be understood that any means or method for extracting a particular tap measurement from a detector-output can be used, such as using frequency division multiplexing.

While presently less preferred due to increased complexity, it is contemplated that the magnitude of the output of integrator 208 could also be used to provide further information to determine the amount by which each tap T is to be steered, in addition to using the polarity of the integrated signal to determine the direction the tap T should be steered. In such a case, instead of adjusting the amount by a preselected increment, a variable increment can be selected depending upon the magnitude of the output.

It is also contemplated that the size of the increment can vary, in a preselected manner, between start up of the adaptive circuit and normal operation of the adaptive circuit. For example, at start up and for a given number of iterations, amplifier 20 of FIG. 1 can employ an increment/decrement size of 5 units, followed by an increment/decrement size of 3 units for another given number of iterations, then followed by an increment/decrement size of 2 units for another given number of iterations, after which an increment/decrement size of 1 unit is employed. This should allow faster convergence of the amplifier at start up.

The present invention provides a novel feed forward amplifier that includes a method and apparatus for steering the gain and phase adjustment such that each tap within the gain and phase adjusters is adjusted at substantially the same time to converge towards an optimum operating setting. Convergence towards the optimum settings are therefore obtained substantially faster and/or more accurately than prior art feed forward amplifiers. Each tap can have a tracer signal, which is orthogonal to other tracer signals, applied to the signal paths through the amplifier. The respective tap measurement is extracted and employed by each tap controller to appropriately alter the respective tap steering signal.

The above-described embodiments of the invention are intended to be examples of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention which is defined solely by the claims appended hereto. 

1. A feed-forward amplifier having a signal cancellation loop including a cancellation node, comprising: a gain controller and a phase controller, each controller for providing a discrete tap steering signal and modulating the corresponding tap steering signal with a discrete tracer signal that takes on a preselected sequence of values, the sequence chosen so that the tracer signal is mutually orthogonal to each other tracer signal over a preselected period; a gain and phase adjuster connected to the outputs of the controllers for providing a controlled gain change and phase shift in the signal cancellation loop, the magnitude of the gain change and phase shift controlled by the corresponding tap steering signals presented to the gain and phase adjuster by the controllers; and a detector, the input of which is connected to the cancellation node and the output of which is connected to the controllers, the detector outputting a measure of the envelope of the signal at the cancellation node, wherein after the preselected period new values for the tap steering signals presented to the gain and phase adjuster by the controllers are obtained by multiplying detector output by the respective tracer signal, each over the respective preselected period, summing each resulting series of values, and changing the tap steering signals to be modulated and presented to the gain and phase adjuster in accordance with the values of the respective sums.
 2. The feed-forward amplifier of claim 1, wherein each tap steering signal is increased or decreased depending upon the polarity of the corresponding sum.
 3. The feed-forward amplifier of claim 1, wherein the tap steering signal presented to the gain and phase adjuster is left unchanged if the corresponding sum is zero or within a preselected range about zero but, if the corresponding sum is outside the preselected range about zero, is increased or decreased depending upon the polarity of the corresponding sum.
 4. The feed-forward amplifier of claim 3, wherein a tap steering signal is increased if the corresponding sum is positive and decreased if the corresponding sum is negative.
 5. A feed-forward amplifier, comprising: an input port; a first main path splitter, the input of which is connected to the input port so that when an input signal applied to the input port it is split by the first main path splitter into a main signal and a feed-forward signal; a main signal path gain and phase adjuster, the input of which is connected to the first output of the first main path splitter, the main signal path gain and phase adjuster having a gain-control input tap and a phase-control input tap configured so that the voltage levels on the taps control the amplitude and phase of the main signal; a main amplifier, the input of which is connected to the output of the main signal path gain and phase adjuster; a second main path splitter, the input of which is connected to the output of the main amplifier; a feed-forward signal path delay element, the input of which is connected to the second output of the first main path splitter, the delay imposed by the feed-forward signal path delay element selected to approximately match the delay in the main signal caused by the main amplifier; a feed-forward path coupler, the first input of which is connected to the output of the feed-forward signal path delay element; a connector/attenuator connecting the second output of the second main path splitter to the second input of the feed-forward path coupler, the attenuation selected so that the undistorted portion of the main signal provided to the feed-forward path coupler is approximately cancelled out by the feed-forward signal; a feed-forward path splitter, the input of which is connected to the output of the feed-forward path coupler; a detector, the input of which is connected to the second output of the feed-forward path splitter; a gain controller, the input of which is connected to the output of the detector and the output of which is connected to the gain-control input tap; and a phase controller, the input of which is connected to the output of the detector and the output of which is connected to the phase-control input tap, wherein: each of the controllers modulates the voltage level on its respective output with a discrete low level signal that takes on a preselected sequence of values, the sequence chosen so that each low level signal is mutually orthogonal to each other low level signal over a preselected period; the detector outputs a measure of the envelope of the signal at the input of the feed-forward path splitter; and each controller multiples the signal received from the detector by the low level signal with which it modulated the tap to which it is connected, in each case over the preselected period, sums the resulting series of values over time, and changes the voltage level on its respective tap in accordance with the value of the sum.
 6. The feed-forward amplifier of claim 5, wherein each voltage level is increased or decreased depending upon the polarity of the corresponding sum.
 7. The feed-forward amplifier of claim 5, wherein the voltage level presented to the gain and phase adjuster is left unchanged if the corresponding sum is zero or within a preselected range about zero but, if the corresponding sum is outside the preselected range about zero, is increased or decreased depending upon the polarity of the corresponding sum.
 8. The feed-forward amplifier of claim 7, wherein each voltage level is increased if the corresponding sum is positive and decreased if the corresponding sum is negative.
 9. The feed-forward amplifier of claim 8, wherein the low level signals vary in polarity but not in magnitude.
 10. The feed-forward amplifier of claim 9, wherein the low level signals are chosen to be pseudo noise sequences.
 11. The feed-forward amplifier of claim 9, wherein the low level signals are chosen to be Walsh codes.
 12. The feed-forward amplifier of claim 11, wherein each output voltage level is changed in proportion to magnitude of the respective sum.
 13. A feed-forward amplifier having a signal cancellation loop including a cancellation node at which a signal is to be minimized, comprising: a controller for providing a tap steering signal and modulating the tap steering signal with a tracer signal that takes on a preselected sequence of values over a preselected period; an adjuster connected to the output of the controller for providing a controlled change in a characteristic of the signal cancellation loop that results in a change in a measure of the envelope of the signal at the cancellation node, the magnitude of the change in the characteristic controlled by the modulated tap steering signal presented to the adjuster by the controller; and a detector, the input of which is connected to the cancellation node and the output of which is connected to the controller, the detector for outputting the measure of the envelope of the signal at the cancellation node, wherein after the preselected period a new setting for the tap steering signal is obtained by multiplying the detector output by the tracer signal, summing the resulting series of values, and changing the tap steering signal to be modulated and provided to the adjuster in accordance with the value of the sum.
 14. The feed-forward amplifier of claim 13, wherein a tap steering signal is increased or decreased depending upon the polarity of the corresponding sum.
 15. The feed-forward amplifier of claim 13, wherein the tap steering signal presented to the gain and phase adjuster left unchanged if the corresponding sum is zero or within a preselected range about zero but, if the corresponding sum is outside the preselected range about zero, increasing or decreasing the tap steering signal depending upon the polarity of the corresponding sum.
 16. The feed-forward amplifier of claim 15, wherein a tap steering signal is increased if the corresponding sum is positive and decreased if the corresponding sum is negative.
 17. The feed-forward amplifier of claim 15, wherein the tap steering signal is changed in proportion to magnitude of the sum.
 18. The feed-forward amplifier of claim 17, wherein the adjuster is a gain adjuster and the characteristic is gain in the gain adjuster.
 19. The feed-forward amplifier of claim 17, wherein the adjuster is a phase adjuster and the characteristic is phase change in the phase adjuster.
 20. The feed-forward amplifier of claim 17, wherein the tracer signal is chosen to be a pseudo noise sequence.
 21. The feed-forward amplifier of claim 17, wherein the tracer signal is chosen to be a Walsh code.
 22. A method for operating an adaptive control circuit having a plurality of control input taps, the method comprising, for each control input, the steps of: detecting a signal, including a tracer signal, from the adaptive control circuit; extracting a measurement from the tracer signal in the detected signal; determining an appropriate input to be applied to the control input to improve operation of the adaptive control circuit; creating a tracer signal for the control input, the created tracer signal being orthogonal to the tracer signals created for each other control input; and combining the tracer signal and the determined input and applying the resulting signal to the control input.
 23. The method according to claim 22 wherein the adaptive control circuit comprises an amplifier portion of a feed forward amplifier having a pair of input control taps for a first gain-and-phase adjuster and a second pair of control input taps for a second gain and phase adjuster.
 24. The method according to claim 22 wherein the tracer signals are Walsh codes.
 25. The method according to claim 22 wherein the tracer signals are pseudo noise sequences.
 26. The method according to claim 22 wherein the tracer signal and the determined input are combined by applying the tracer signal to the determined input as a dither.
 27. An adaptive circuit comprising: at least two adjusters, each adjuster including at least one control input to alter the operation of the circuit; at least one signal generator to create at least two tracer signals, each created tracer signal being orthogonal to each other created tracer signal; at least two controllers, each controller operable to output a control signal to at least a respective one of the control inputs of the at least two adjusters, a different orthogonal tracer signal from the at least one signal generator being applied to each respective control signal as a dither; and at least one detector operable to extract a composite signal from the circuit and to apply the composite signal to the at least two controllers, each controller being responsive to the applied signal to extract at least one orthogonal tracer and to alter the respective control signal to converge operation of the circuit to an optimal or near optimal configuration.
 28. The adaptive circuit as claimed in claim 27, wherein the adaptive circuit is a feed forward amplifier.
 29. The adaptive circuit as claimed in claim 28, wherein the at least two adjusters operate to adjust the phase and gain of a signal passed through them and each of the at least two adjusters includes a phase control input tap to control the phase adjustment and a gain control input tap to control the gain adjustment.
 30. The adaptive circuit as claimed in claim 29, further including at least two detectors, each of the at least two detectors extracting at least two composite signals and applying the composite signals to a respective one of the at least two controllers, each controller being responsive to the applied signal to extract at least one orthogonal tracer and alter the respective control signal to converge operation of the circuit to an optimal or near optimal configuration.
 31. The adaptive circuit as claimed in claim 29 wherein the orthogonal tracer signals are Walsh codes.
 32. The adaptive circuit as claimed in claim 29 wherein the orthogonal tracer signals are pseudo noise sequences. 